Updating package channels is done with
sudo nix-channel --update
Rebuilding the main system is done with
sudo nixos-rebuild switch
and upgrading with
sudo nixos-rebuild switch --upgrade
Garbage is collected with
sudo nix-collect-garbage -D
A package can be installed for the current user with
nix-env -iA pkgs.Python34Packages.pandas
Nox can also be used
nox pandas
Open a nix-shell with a one or multiple packages
nix-shell -p python34Packages.pandas python34Packages.scipy
Open a nix-shell with one or multiple packages based on a modified nixpkgs repository
nix-shell -I nixpkgs=/path/to/nixpkgs -p python34Packages.newpackage python34Packages.pandas
To test whether all dependents still function with the new package, you can use
nox-review wip
if the changes haven't been commited yet.